Captain Kirk first encountered Gary Seven on twentieth-century Earth. Now Seven, a time-traveling operative for unknown alien forces, makes a surprise visit to the USS Enterprise. Kirk is on an urgent mission to bring relief to a disaster-ravaged planet, but Seven has an agenda of his own -- and he's not above hijacking the Starship Enterprise and sending it on a perilous journey deep into the heart of the Romulan Empire.
Kirk must dare to trust Gary Seven once again, as he confronts the possibility that the enigmatic stranger may bring death and destruction to Kirk's own era.
Romulan Commander Dellas of the Tal Shiar witnesses the failed assassination attempt on the Federation president at the Khitomer conference, then herself assassinates Captain Spock.
After ensuring the success of the Apollo 11 moon landing, Gary Seven is alerted to a disruption of the timeline. He, Isis, and Roberta Lincoln transport themselves through time and space to 2269, the apparent divergence point, aboard the Enterprise.
2269 Stardate 6021.4
The Enterprise, en route to deal with an environmental disaster threatening the Federation colony on Duwamish, intercepts Seven's transporter beam. He insists on Kirk's help in carrying out a vital mission within Romulan space, though he refuses to share any of the details. When Kirk refuses, Seven imbalances the starship's warp engines, creating a wormhole that delivers the vessel deep within the Empire. The ship soon comes under attack by a squadron led by Commander Motak of the Gladiator, and is forced to flee deeper into Romulan space. Sensors detect an uninhabited star system that apparently contains a cloaked planet and Kirk decides to investigate, fearing a secret Romulan base and an incredible Romulan technological advance. The Enterprise hides from the Gladiator within the cloaking field while Kirk, Sulu, and Chekov beam to the surface. Seven escapes from the brig and invites himself on the landing party. Kirk tries to have him returned to the Enterprise, but a force field blocks transporters and communications.
Seven finally shares minimal details of his mission—his contemporary in this area and region, Supervisor 146 (aka Septos), has been discovered and captured by Romulan forces, and plan to use their newfound advanced technology to alter the timeline. The team meets up with Septos' pet/partner, a large sentient feline named Osiris. While Sulu and Chekov create a diversion, Kirk, Seven, and Osiris slip inside the captured base, and Septos escapes from Dellas' intensive interrogation and reach the control center.
In orbit, Spock prepares to abandon the landing party and escape Romulan territory to safeguard the ship and crew, but Roberta uses her superior technology to seize control of the ship. Spock conducts a mind-meld so that both sides can trust each other and learns of his own future assassination, though he convinces Roberta to return control of the ship. The Enterprise departs the cloaking field, drawing the Gladiator away from the planet and ultimately disabling the battlecruiser by tying Roberta's interface cube into a torpedo's sensors. The ship then returns to the planet to rescue the landing party.
Kirk, Seven, and Osiris find Septos just as Dellas beams in and murders him, then Osiris. A firefight ensues, but Dellas wins out by overloading her disruptor and stunning them all. The paranoid Dellas sends her troops away, guarding Kirk and Seven herself until using the transporter to travel to 2293 to kill Spock. Seven sets the base's autodestruct before following her into the future, leaving Kirk to hold off the rest of the Romulan troops. He narrowly succeeds and returns to 2269 moments before the explosion, but Isis, aboard the Enterprise, reconfigures the transporter to rescue everyone from the planet. The base is destroyed, keeping its advanced technology out of Romulan hands, and Spock mind-melds with Dellas and her technologist, Vithrok, to remove all knowledge of the same. Seven repeats his wormhole trick to deliver the Enterprise to Duwamish several days in the past, allowing the crew to complete their vital mission, before returning himself, Isis, and Roberta to 20th century Earth.
- Azetbur • Christine Chapel • Pavel Chekov • Clark • Dellas • Sheryl Gates • Greenburg • Isis • James T. Kirk • Roberta Lincoln • Leonard McCoy • Motak • Osiris • Pardek • Esteban Rodriguez • Sarek • Montgomery Scott • Schultz • Septos • Gary Seven • Spock • Hikaru Sulu • Nyota Uhura • Valeris • Vithrok • Worf, father of Mogh
- Referenced only
- Aladdin • Neil Armstrong • Clyde Barrow • James Bond • Cho • Bob Dylan • Sean Finnegan • Gorkon, son of Toq • Phillip Green • Guardian of Forever • George Harrison • Robert A. Heinlein • Jimi Hendrix • J. Edgar Hoover • I-Chaya • Edith Keeler • John F. Kennedy • Jacqueline Kennedy • Martin Luther King, Jr. • Kollos • Janice Lester • David Marcus • Peter Max • Paul McCartney • Midnight • Number Six • Bonnie Parker • Emma Peel • Christopher Pike • Ebenezer Scrooge • Rod Serling • Khan Noonien Singh • Tolian Soran • Benjamin Spock • Surak • T'Pring • Mao Tse-Tung • Tepesch • Zarabeth • Zoe
Starships and vehicles
- USS Enterprise (Constitution-class) • ChR Gladiator (D7-class) • unnamed Romulan starships
- Referenced only
- Apollo 11 • RMS Queen Mary • Saturn rocket
- 811 East 68th Street • Camp Khitomer • Duwamish • Duwamish system • Earth • Khitomer • New York City • United States of America
- Referenced only
- Alamo • Andromeda system • Argelius II • Barbaros IV • Buckingham Palace • Coney Island • Deep Space 5 • District of Columbia • East Village • Ekos • Eminiar VII • Gothos • Great Wall of China • Iowa • Janus VI • Luna • Manhattan • Mirror Lake Elementary School • mirror universe • Moscow • Mount Seleya • Neutral Zone • Organia • Puget Sound • Pyriss VII • Remus • Romulus • Sigma Draconis VI • Skylab • Taurus II • Three Mile Island • Vulcan
Races and cultures
- Human • Klingon • Martian • Romulan • Tellarite • Vulcan • Xela
- Referenced only
- Andorian • Eymorg • Gorn • Horta • Organian • Tholian • Triclopian
States and organizations
- Aegis • Klingon Empire • NASA • Romulan Star Empire • Soviet Union • Starfleet • Starfleet Academy • Tal Shiar • United Federation of Planets • United States of America • University of Moscow • Vulcan Science Academy
Ranks and titles
- ambassador • captain • centurion • chairman • chancellor • chief engineer • commander • colonel • diplomat • doctor • ensign • helmsman • lieutenant • minister • nurse • Praetor of the Romulan Star Empire • president • President of the United Federation of Planets • proconsul • science officer • secretary • security officer • Supervisor 146 • Supervisor 194 • yeoman
Science and technology
- AIDS • alternate timeline • anabolic protoplaser • artificial gravity • astrogator • Beta-5 • Beta 7 computer • blood • Cerenkov radiation • chronometer • cloaking device • clone • communicator • computer • cordrazine • deflector shield • disruptor • duranium • emergency beacon • Excedrin • dental fillings • fire extinguisher • food synthesizer • force field • gravimetric distortion • hypospray • intercom • magnetic lock • medical tricorder • mind-sifter • multipurpose controller • nova • phaser • photon torch • photon torpedo • satellite • sensor • servo • shield • stasis field generator • television • time travel • transporter • tricorder • turbolift • universal translator • viewscreen • virus • warp nacelle • wormhole
- 1960s • 1968 • 1969 • 2269 • 2293 • 20th century • 23rd century • 24th century • Age of Aquarius • apartment • apple • assassination • The Avengers • barrel • beard • The Beatles • belt • The Brain Eater • bridge • brig • British • captain's chair • captain's log • cat • chewing gum • Chinese • cockroach • cocktail glass • coffee • command module • corridor • couch • Cuban Missile Crisis • cybernaut • dinosaur • Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb • Earth Cold War • emergency ration • espionage • Fail-Safe • fire • Fresca • Funny Girl • The Girl from U.N.C.L.E. • Grand Coulee Dam • handbag • helmet • history • hornet • jacket • Japanese • jeans • Jolan tru • Jovian Triathalon • jungle • Khitomer Conference • Kleenex • landing party • logic • mind meld • The Monkees • movie • Mission: Impossible • money • necktie • Nobel Prize • nutrient bar • onkian • P.F. Flyers • pineapple • pizza • Planet of the Apes • plomeek soup • popcorn • Prime Directive • The Prisoner• quarters • rain • red alert • robe • Romulan ale • Russian • science fiction • Scottish • sector • sickbay • Space Age • Stranger in a Strange Land • Treaty of Algeron • toadstool • tree • tribble • T-shirt • 2001: A Space Odyssey • uniform • Village Voice • Vulcan nerve pinch • Watergate • Woodstock • yellow alert • Zorro
- TOS episode Assignment: Earth
- TOS episode Turnabout Intruder
- TOS film Star Trek: The Motion Picture
- TOS film Star Trek VI: The Undiscovered Country
- TOS novel The Eugenics Wars: The Rise and Fall of Khan Noonien Singh, Volume 1
- TOS novel The Eugenics Wars: The Rise and Fall of Khan Noonien Singh, Volume 2
- TNG episode Unification, Part I
- TNG episode Unification, Part II
- TAS episode The Counter-Clock Incident
- This novel is a sequel to TOS episode: "Assignment: Earth".
- The 2269 sequences take place a week after the events of TOS episode: "Turnabout Intruder" and almost three years after those of TOS episode: "The City on the Edge of Forever".
- After the Enterprise was force through a wormhole, Kirk worried that the distance to return could take 75 years. He even thought it could make quite an adventure. This was in reference to Star Trek: Voyager.
20th century references
- Roberta Lincoln tells Spock that he reminds her of an extraterrestrial from the science fiction film The Brain Eaters. This is a reference to a real life 1958 film in which Leonard Nimoy made a brief appearance. However, he did not play an alien in the film but a human character named Professor Cole.
- Roberta refers to Rod Serling, the creator of The Twilight Zone. In real life, William Shatner, Leonard Nimoy, James Doohan and George Takei all made guest appearances on the series, as did numerous other Star Trek actors. She also refers to Mission: Impossible, in which Shatner and Nimoy likewise appeared.
- Roberta's comment regarding Chekov's resemblance to Davy Jones is an in-joke, referring to the fact that after Walter Koenig was cast in the second season of Star Trek: The Original Series, he was made to look like Jones in order to draw in younger viewers. The ploy worked.
- The Girl from U.N.C.L.E.: Lincoln thinks to herself, "Yeah, that's me. The Girl from U.N.C.L.E."
- James Bond and Mission: Impossible: Roberta tells Kirk that Gary Seven "...works on a strictly need-to-know basis, you know? James Bond style. For your eyes only and all that. This tape will self-destruct in five seconds..." Kirk has never heard of the James Bond franchise.
In addition to merely mentioning TV series and films from the 20th Century, this novel also references several in terms of indicating that they could have analogous events within the Star Trek universe:
- The Avengers: Spock says that Seven and Lincoln contributed to "the defeat of the so-called 'cybernauts' in conjunction with a pair of British intelligence operatives". Lincoln thinks to herself, "I bet Mrs. Peel never has to go poking around under the furniture."
- Kolchak: The Night Stalker and The Questor Tapes: Roberta tells Spock, "There was this other time, while we were teamed up with this wise guy reporter from Chicago, when Seven actually sneaked in and out of the Pentagon with the top secret plans for a new type of robot soldier. The Quasar Tapes, or something like that."
- The Prisoner: "All this covert infiltration reminded [Seven] of that time he and Isis had attempted to liberate a former British intelligence agent from the artificial village where he was being held captive as part of an elaborate psychological conditioning experiment. That mission had ended badly, he remembered, primarily because he had underestimated the forces arrayed against them."
- The Andromeda Strain: Spock says that Seven and Lincoln contributed to "the destruction of fourteen deadly biological weapons, including one spaceborn virus".
- James Bond: Seven recalls the time Lincoln "...had outwitted that power-hungry megalomaniac with the white Persian kitten."
- Vejvoda, Jim and Phil Pirrello. "Star Trek: The Original Series - Season 2 Review." IGN.com, 
Heart of the Sun
|TOS numbered novels||Next novel:|
The Black Shore
|Pocket Books Timeline||Next adventure:|
"As Others See Us"
|Memory Beta Chronology||Next adventure:|
"As Others See Us"
|The above chronology placements are based on the primary placement in 2269.|
The Pocket Books Timeline and Memory Beta Chronology place events from this story in other timeframe(s):
Star Trek VI: The Undiscovered Country
Prologue, Chapter 19 & Epilogue
|Next Pocket adventure:|
"One Last Adventure"
Next MB adventure:
"Do Not Close Your Eyes"
Prologue & Epilogue
|Media featuring Gary Seven|
|Miniseries||The Peacekeeper • Convergence • The Eugenics Wars • Assignment: Earth|
|Novels||Assignment: Eternity • The Rise and Fall of Khan Noonien Singh, Volume 1 • The Rise and Fall of Khan Noonien Singh, Volume 2 • From History's Shadow • Elusive Salvation|
|Short stories||"The Aliens Are Coming!" • "Seven and Seven" • "Assignment: One" • "Rocket Man" • "Time Line"|
|Comics||"The Peacekeeper, Part One" • "The Peacekeeper, Part Two" • "Split Infinities" • "Future Imperiled" • "Brighter Than a Thousand Suns" • "Yesterday, Today and Tomorrow" • "My Name Is Legion" • "We Have Met the Enemy..." • "Too Many Presidents" • "Ah-Ha!" • "Medics" • "Hosts" • "1971/4860.2" • "An Unexpected Yesterday" • "Year Five, Issue 11" • "Year Five, Issue 12" • "Year Five, Issue 15" • "Year Five, Issue 16" • "Year Five, Issue 17" • "Year Five, Issue 21" • "Year Five, Issue 22"|